A photomask is a plate with holes or transparencies that allow light to shine through in a defined pattern. Photomasks may be utilized for production of integrated circuit devices. For instance, a defined pattern on a photomask may be transferred to a resist arranged on a semiconductor wafer. Photomasks may be referred to as photoreticles or reticles.
Various inspection techniques may be utilized to find possible contamination (non-pattern) defects on reticles. For example, for reticles containing multiple identical dice, one of them may be utilized as a reference, which may be used to compare against another die with the same pattern in order to detect possible contaminations. However, such types of inspections may only be useful when multiple identical dice are available. If the reticle is a single die reticle, such inspection techniques are not applicable as there is no reference available.
Different inspection techniques may be utilized for reticles without repeating dice. In one example, if the design information for a given reticle is available, a high resolution scan of the reticle may be compared against the design information to detect possible contaminations. However, a high resolution scan is compute intensive and the design information may not always be available and/or accessible.
Cell-to-cell inspection is another technique that may be utilized for reticles without repeating dice. Local repeating cells (if available) may be used as a local reference to detect possible contaminations. However, cell-to-cell inspections can only over the portion of the reticle that has repeating cells of patterns (if any).
The STARlight™ inspection tool provided by KLA-Tencor Corporation of Milpitas, Calif. is another example. STARlight inspection tools may directly or indirectly use material transmission and reflection characteristics as references to detect possible contaminations. However, such type of inspection tools may be relatively slow, and may be challenged with very complex patterns having small features.
Therein lies a need for a fast and effective method for detecting contamination defects on single-die or multi-die reticles.